Digital data, such as digital images, moving picture images or videos, contain a lot of information (represented by pixels) that is redundant for the human visual system. Removing this redundant information reduces the size of the digital data, such as images and videos, so that the digital data may be compressed. Thus, it is desirable to have a way in which that redundant data may be removed automatically. Furthermore, it is desirable to be able to reduce the redundancy in compressed data.